equatorium: instrument to determine the longitude of one or more of the planets at any given time.

equinoctial: relating to or based on the equator, or relating to the equinox.

equinoctial dial: sundial where the hour plate or circle is set parallel to the equator, see article on the sundial.

equinoctial ring dial: type of sundial, included as an equinoctial dial, comprising two pivoted rings and a bridge for adjusting for solar declination, or of three rings.

equinox: either of two points on the celestial sphere where the equator meets the ecliptic, representing the position of the sun when it is 90 degrees from the poles, or the two dates in the year when the sun is in this position in its annual cycle.

folding rule and level: a compound instrument combining the functions of both a folding rule and level.

gauging rod: measuring stick, usually with a scale to provide a direct reading of volume, such as the liquid content of a barrel, or the weight of a cannonball.

geographical astrolabe: form of astrolabe, where the lower plate is projected for the earth, while the rete includes the ecliptic.

geographical planisphere: map of the earth, produced by geometrical projection of a sphere on to a flat surface. Included as the more prominent part of the geographical astrolabe.

geometrical square: form of quadrant, with sides divided equally and having an alidade at one corner, used for measuring angles in terms of ratios in the manner of a shadow square on the back of an astrolabe.

globe dial: form of sundial, where the hour lines are on the outer surface of a sphere.

gnomon: the part of a sundial that casts the shadow for indicating the time.